Washing towers are used for the desulphuration of flue gases. In order to prevent the escape of washing liquid droplets together with the cleaned flue gas, droplet separators are installed towards the outlet of the washing tower, sometimes also in a special housing downstream of the washing tower. For example, a typical configuration according to which flue gas and washing liquid are directed in cross-flow has a two-stage droplet separator. The content of solid matter of the droplets trapped by the droplet separator remains adhered to the surface of the separator with a certain percentage and can result there in an incrustation affecting the function. In order to avoid encrustation droplet separators are provided with a spray cleaning system.
At first, washing towers were provided with only one droplet separator stage. However, soon one had to recognize that a second droplet separator stage was necessary for substantially avoiding the escape of droplets disturbing the operation of following components, such as blowers or heaters for the purified gas. Meanwhile, long term operational experiences show that an even stronger reduction of the droplet output of the washing tower makes economic sense. Thus, repair costs of the following components can be avoided which can easily reach ten times the installation costs for a third droplet separator stage. Furthermore, the emission of coarse particles with the flue gas is strongly reduced since a reduced droplet content in the purified gas is connected with a reduced input of solid matter into the tract of the purified gas is connected. The emission of frequently corrosive coarse particles (d&gt;0.5 mm) together with the flue gas resulted in substantial claims of compensation at some places.
With new installations the arrangement of a third droplet separator stage does not cause fundamental problems and can be realized with little additional cost. However, with old installations the third droplet separator stage can only be connected with very high costs. In many cases it can be only realized with low costs by an extreme compact construction. However, it is necessary to inspect the droplet separators from time to time. On account of this reason in the past the droplet separators were installed with a distance from one another sufficient for the access of the intermediate space. In this intermediate space the cleaning nozzles for the droplet separator are disposed.
However, in many cases the available space for the installation of a third droplet separator stage is so small that the principle of "accessibility of the intermediate space" has to be given up or very high costs for an extensive reconstruction of the washer head or for the installation of a special droplet separator housing have to be accepted.